easy IF Statement always False in bash script

I am an absolut beginner with the bash script. I have a simple if statement but i didn't get it to run as it should.

if [[ "$body" -gt "0" ]]
then
     echo $body
     echo is greater than 0
else
     echo $body
     echo is equal 0
fi

the output is:

4
is equal 0

I have no more idea. Could you help?